U.S. Pat. No. 4,921,071, which is incorporated herein by reference in its entirety, discloses a transparent container mounted to the inner transom wall of a boat and connected to the oil passages in a stern drive unit. The container is provided with a removable cap having a one-way valve of the Vernay type therein. The valve prevents outward leakage of lubricant fluid from the container, but permits inward passage of air so that, during engine and drive unit cooling, lubricant can be sucked back into the system through the drive housings. The cap may be provided with a lubricant level warning device which extends downwardly into the container.
U.S. Pat. No. 6,227,921, which is incorporated herein by reference in its entirety, discloses a marine propulsion device, such as an outboard motor, provided with an oil measuring gauge or dipstick which is accessible by the operator of the outboard motor without having to remove the cowl from the device. A first end of the dipstick extends through a dipstick tube into the oil sump of the outboard motor and a second end of the dipstick is connected to a handle that extends through the cowl. The handle is shaped to be retained in a hole formed through the cowl in such a way that the hole is sealed by a portion of the handle to prevent water from passing into the engine compartment through the cowl. A dampening mechanism is provided to dampen vibrations that would otherwise be transmitted between the handle and the dipstick.
U.S. patent application Ser. No. 13/313,930, filed Dec. 7, 2011, discloses systems and methods for determining oil level in a marine outboard motor having an internal combustion engine. A control circuit determines whether oil has drained back into a sump from the internal combustion engine. An oil sensor senses an oil level in the sump. The control circuit calculates a characteristic of the actual oil level of the outboard motor based upon the oil level after the oil has drained back into the sump and based upon a trim position of the outboard motor.